1. Field of the Invention
The present invention relates to a ceramic electronic component and a method for manufacturing the same. In particular, the present invention relates to an embedded ceramic electronic component, which is arranged to be embedded in a wiring board, and a method for manufacturing the same.
2. Description of the Related Art
In recent years, along with miniaturization and thickness reduction of electronic apparatuses, e.g., cellular phones and portable music players, wiring boards mounted on the electronic apparatuses have been miniaturized.
Japanese Unexamined Patent Application Publication No. 2002-100875 discloses a method for miniaturizing a wiring board in which a ceramic electronic component is embedded inside of a wiring board and, in addition, wiring to the ceramic electronic component is formed by using a via hole disposed on the ceramic electronic component. According to this method, it is not necessary to provide a region on the surface of a wiring board for mounting a ceramic electronic component and, in addition, it is not necessary to provide a region for wiring to the ceramic electronic component separately from the region for mounting the ceramic electronic component. Consequently, a wiring board including a built-in component can be miniaturized.
The via hole for connecting a ceramic electronic component is formed by using, for example, a laser, e.g., a CO2 laser. When the via hole is formed using the laser, the laser is applied directly to an external electrode of the electronic component. Therefore, it is preferable that the external electrode includes a Cu plating film to reflect the laser at a high reflectance. This is because if the reflectance of the external electrode with respect to the laser is low, the laser penetrates to the inside of the ceramic electronic component and, thereby, the ceramic electronic component may be damaged.
Regarding the ceramic electronic component embedded in the inside of the wiring board, a reduction in profile has been extremely desirable from the viewpoint of thickness reduction of the wiring board.
For a method for reducing the profile of the ceramic electronic component, it is preferable to fire an underlying electrode layer located immediately above a ceramic element assembly, among external electrodes, at the same time with the ceramic element assembly including internal electrodes, that is, to form through cofiring. This is because the maximum thickness of the underlying electrode layer can be reduced by the above-described method as compared to when the underlying electrode layer is formed by, for example, baking an electrically conductive paste applied through dipping.
In this regard, when the underlying electrode layer is formed through cofiring, it is necessary to increase the content of a ceramic bonding material, e.g., a ceramic material, in the underlying electrode layer in order to ensure high adhesion between the ceramic element assembly and the underlying electrode layer. However, if the content of the ceramic bonding material in the underlying electrode layer is increased, the content of the metal component in the underlying electrode layer is decreased. Consequently, the adhesion between the underlying electrode layer and a plating layer disposed on the underlying electrode layer is reduced. Therefore, there is a problem in that the reliability of the electronic component is degraded.